Assessment of EEG Frequency
Dynamics Using Complex Demodulation
R. DRAGANOVA, D. POPIVANOV
Institute of Physiology, Bulgarian Academy of
Sciences, Sofia, Bulgaria
Received October 20, 1997
Accepted September 8, 1998
Summary
The complex demodulation (CD) approach was applied to human EEG
recorded during a cognitive task performance, including
voluntary goal-directed movements. The standard CD algorithm was
extended by a simple procedure using frequency histograms and
power spectra to select the characteristic frequencies of EEG
segments around the task performance. In the majority of
records, amplitude modulation was found, which decreased or
disappeared in the period prior to and at the very beginning of
the task performance. It was found that the decrease of
modulation in fast beta and gamma components begins
approximately one second before that of the alpha components.
Frequency modulation appeared in some records at the end of the
task in beta and gamma components. The results showed that a
cognitive task performance is accompanied by non-linear
processes in the frequency components of EEG. These dynamic
changes could extend the findings of event-related
desynchronization obtained by linear methods.
Key words
Complex demodulation · EEG · Hilbert transformation · Voluntary
goal-directed movements
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